1. Field of the Invention
This invention pertains generally to a diplexer, and more particularly to diplexer utilizing composite right/left-handed (CRLH) phase advance/delay lines in combination with a hybrid coupler.
2. Description of Related Art
Modern communication systems often require dual-band operation, and therefore, diplexers are essential elements in transceiver modules for the electromagnetic spectrum. A diplexer is a form of frequency selective demultiplexer having one input and two outputs. One application of a diplexer allows two different devices at different frequencies to share a common communications channel. Diplexers have a wide range of applications for signal transmission in the electromagnetic spectrum. For decades, studies on diplexers attracted industry attention with the results of numerous researchers reported.
However, these diplexers have conventionally comprised two bandpass filters, each of which is responsible for the respective frequencies in dual-band schemes. More recently diplexers have been proposed which comprise waveguide filters. Although low insertion loss and high isolation were obtained from these waveguide filter diplexers, parametric optimization on the three-port junction connecting the filters and the requisite performance tuning are time-consuming processes. In order to suppress higher-order harmonics of filters, stepped-impedance resonators (SIRs) were utilized. In response to this arrangement, the spurious harmonic responses were controlled at the expense of design complexity. Even though channel isolation in diplexer design can perhaps be enhanced, it typically requires interconnection of additional circuit elements, such as tapped open stubs, and λ/4 microstrip lines in front of the filters.
Accordingly, a need exists for an apparatus and method for designing compact diplexers which simplify the design complexity by engineering the dispersion relation of the structure. These needs and others are met within the present invention, which overcomes the deficiencies of previously developed diplexing methods and apparatus.